An efficient catalyst is a key in industrialization of dehydration of alcohols. One of the early catalysts employed for the dehydration of ethanol was alumina. This catalyst is relatively cheap but needs low space velocity, high reaction temperature and makes a lot of ethane, which needs to be separated. Zeolites, particularly phosphated zeolites, solves a problem with catalyst activity and provide with directly polymer grade or close to polymer grade ethylene fraction. Catalysts comprising a phosphorus modified zeolite (the phosphorus modified zeolite is also referred as P-zeolite) are known. The following prior arts have described various methods to make said catalysts.
US 2006 106270 relates to the use of a dual-function catalyst system in the hydrocarbon synthesis reaction zone of an oxygenate to propylene (OTP) process that operates at relatively high temperatures preferably with a steam diluent and uses moving bed reactor technology. The dual-functional catalyst system comprises a molecular sieve having dual-function capability dispersed in a phosphorus-modified alumina matrix containing labile phosphorus and/or aluminum anions. It is explained that the hydrothermal stabilization effect that is observed when this phosphorus-modified alumima matrix is utilized is caused by migration or dispersion of phosphorus and/or aluminum anions from this matrix into the bound molecular sieve. These anions are then available to repair, anneal and/or stabilize the framework of the molecular sieve against the well-known dealumination mechanism of molecular sieve framework destruction or modification that is induced by exposure to steam at temperatures corresponding to those used in the OTP reaction zone and in the regeneration zone.
U.S. Pat. No. 5,231,064 is directed to a fluid catalyst comprising clay and a zeolite, at least one of which has been treated with a phosphorus containing compound, for example ammonium dihydrogen phosphate or phosphoric acid, and which is spray dried at a low pH, preferably lower than about 3. Said catalysts are deemed to advantageously exhibit reduced attrition.
EP 511013 A2 provides an improved process for the production of C2-05 olefins from higher olefinic or paraffinic or mixed olefin and paraffin feedstock's. In accordance with this prior art, the hydrocarbon feed materials are contacted with a particular ZSM-5 catalyst at elevated temperatures, high space velocity and low hydrocarbon partial pressure to produce lower olefins. The catalysts is treated with steam prior to use in the hydrocarbon conversion. The active catalyst component is phosphorus-containing ZSM-5 having a surface Si/Al ratio in the range 20-60. Preferably, the phosphorus is added to the formed ZSM-5 as by impregnating the ZSM-5 with a phosphorus compound in accordance with the procedures described, for example, in U.S. Pat. No. 3,972,832. Less preferably, the phosphorus compound can be added to the multicomponent mixture from which the catalyst is formed. The phosphorus compound is added in amount sufficient to provide a final ZSM-5 composition having 0.1-10 wt. % phosphorus, preferably 1-3 wt. %.
The phosphorus-containing ZSM-5 is preferably combined with known binders or matrices such as silica, kaolin, calcium bentonite, alumina, silica aluminate and the like. The ZSM-5 generally comprises 1-50 wt. % of the catalyst composition, preferably 5-30 M. % and most preferably 10-25 wt. %. This prior art doesn't concern the dehydration of alcohols to make an olefin having the same number of carbon atoms as the alcohol.
EP 568913 A2 describes a method for preparing a ZSM-5 based catalyst adapted to be used in the catalytic conversion of methanol or dimethyl ether to light olefins, wherein it comprises the following consecutive steps:                mixing a zeolite ZSM-5 based catalyst with silica sol and ammonium nitrate solution,        kneading, moulding, drying and calcining the mixture,        exchanging the modified zeolite with a solution of HCl at 70-90° C.,        drying and calcining the H-modified zeolite,        impregnating the H-modified zeolite with phosphoric acid under reduced pressure,        drying and calcining the P-modified zeolite,        impregnating the P-modified zeolite with a solution of rare earth elements under reduced pressure,        drying and calcining the P-rare earths-modified zeolite,        hydrothermally treating the P-rare earths-modified zeolite at 500-600° C. with water vapour, and        calcining the modified zeolite.        
WO 03 020667 relates to a process of making olefin, particularly ethylene and propylene, from an oxygenate feed, comprising contacting an oxygenate feed with at least two different zeolite catalysts to form an olefin composition, wherein a first of the zeolite catalysts contains a ZSM-5 molecular sieve and a second of the zeolite catalysts contains a zeolite molecular sieve selected from the group consisting of ZSM-22, ZSM-23, ZSM-35, ZSM-48, and mixtures thereof. The ZSM-5 can be unmodified, phosphorus modified, steam modified having a micropore volume reduced to not less than 50% of that of the unsteamed ZSM-5, or various mixtures thereof. According to one embodiment, the zeolite is modified with a phosphorus containing compound to control reduction in pore volume. Alternatively, the zeolite is steamed, and the phosphorus compound is added prior to or after steaming. The amount of phosphorus, as measured on an elemental basis, is from 0.05 wt. % to 20 wt. %, and preferably is from 1 M. % to 10 wt. %, based on the weight of the zeolite molecular sieve. Preferably, the atomic ratio of phosphorus to framework aluminum (i.e. in the zeolite framework) is not greater than 4:1 and more preferably from 2:1 to 4:1. Incorporation of a phosphorus modifier into the catalyst of the invention is accomplished, according to one embodiment, by contacting the zeolite molecular sieve either alone or the zeolite in combination with a binder with a solution of an appropriate phosphorus compound. The solid zeolite or zeolite catalyst is separated from the phosphorus solution, dried and calcined. In some cases, the added phosphorus is converted to its oxide form under such conditions. Contact with the phosphorus-containing compound is generally conducted at a temperature from 25° C. to 125° C. for a time from 15 minutes to 20 hours. The concentration of the phosphorus in the zeolite may be from 0.01 wt. % to 30 wt. %. This prior art discloses a non-formulated P-ZSM-5.
WO 2009 022990 A1 describes a catalyst composition for dehydration of an alcohol to prepare an alkene. The catalyst composition comprises a catalyst and a modifying agent which is phosphoric acid, sulfuric acid or tungsten trioxide, or a derivative thereof. There is no binder.
EP 2348004 A1 relates to the dehydration of ethanol to make ethylene. The catalyst is made by the following process: A ZSM-5 is steamed, P is introduced by contacting the steamed zeolite with an H3PO4 solution under reflux conditions, the P modified zeolite is extruded with a binder, calcium is introduced and the resulting catalyst is steamed two hours at 600° C. This prior art discloses a formulated P-ZSM-5, where at least a part of phosphorous was introduced into zeolite before formulation step.
WO 2009-098262 A1 relates to the dehydration of ethanol to make ethylene. The catalyst is made by the following process: A ZSM-5 is steamed, P is introduced by contacting the steamed zeolite with an H3PO4 solution under reflux conditions, the P modified zeolite is extruded with a binder, there is no final steaming. There is no introduction of calcium.
EP 2082802 A1 relates to various petrochemical processes, the dehydration of alcohols to make an olefin having the same number of carbon atoms as the alcohol is not cited. Among the cited processes are the cracking of olefins and the conversion of oxygenates, e.g. methanol to make a mixture of ethylene, propylene, butenes and various hydrocarbons. The catalyst is made by the following process: A ZSM-5 is steamed, the steamed zeolite is extruded with a binder, P is introduced by contacting the steamed zeolite with an H3PO4 solution under reflux conditions, calcium is introduced in form of metal silicate and the resulting catalyst is steamed two hours at 600° C.
U.S. Pat. No. 4,356,338 relates to the aromatization of hydrocarbon, the dehydration of alcohols to make an olefin having the same number of carbon atoms as the alcohol is not cited. The zeolite (ZSM-5) may be combined with a binder and is treated by a P containing component or steam or both steam and P containing component. The said catalyst has a reduced coking. There is no introduction of metals such as Ca in the catalyst.
A common way to produce a formulated P-zeolite containing catalyst consists in the impregnation of the already pre-formulated zeolite (e.g. the zeolite+ a binder) with P-compounds or phosphorus addition to the reaction medium followed by drying/calcination. This solution is appropriate for high temperature processes like FCC (fluid catalytic cracking), MTO (methanol to olefins conversion) etc. In this case the catalyst is self-equilibrating during regeneration processes occurring at high temperature in presence of steam. On the contrary, in case of alcohols dehydration, low reaction temperature doesn't offer the same opportunity. Moreover, the metals, refractory oxides and binder components may also adsorb the phosphorus interfering and even competing with zeolite. This prevents a proper zeolite phosphatation and requires an excess of phosphorus leading to a partial plugging of microporosity. The presence of the traces of alkali metals adsorbing preferentially the phosphorus could even more perturb the zeolite phosphatation. This often leads to non-selective catalysts due to a poor reproducibility.
The present invention provides a solution to selectively introduction of phosphorus into formulated catalyst (the catalyst+the binder) levelling off the side effects of the binder presence. Thus, the invention discloses that a preparation of a selective catalyst for alcohols dehydration requires a treatment of shaped zeolite advantageously substantially free of alkali metal with phosphorus followed by steaming of the modified solid. The said steam treatment facilitates interaction of zeolite with phosphorus in presence of binder, improve conversion of non-phosphated framework AlIV sites into low acid alumina phase and level off the acidity of P-species adsorbed on a binder and stabilizing phosphorus on the catalyst. This method insures a reproducibility of the preparation and a good catalyst performance.